This disclosure relates generally to communications involving a fob and, more particularly, to managing radio frequency communications between many fobs and vehicles.
Fobs used in active systems may include a button. Actuating the button sends a signal from the fob to a base station within a vehicle, for example. In passive start and entry or “PASE” systems, the fob sends a return signal to the base station in response to a challenge signal from the base station. In one example, actuating a door handle on the vehicle prompts the base station to transmit the challenge signal. In both active and passive systems, the base station initiates an action, such as unlocking the vehicle, in response to signals sent from the fob.
The base station may fail to initiate an action if the signal sent from a fob overlaps a signal sent from another fob. In a passive system, overlapping signals could occur when two users approach a vehicle at the same time. Accordingly, in typical passive systems, each of the fobs is programmed to have a unique time delay before sending their signal to the base station. For example, if a first fob and a second fob both receive a challenge signal from a base station at the same time, the first fob will send a return signal after a 10 millisecond delay and the second fob will send a return signal after a 20 millisecond delay. Delaying the return signals different amounts ensures that the first fob's return signal does not overlap the second fob's return signal.
Base stations are often configured to communicate with eight or fewer fobs. Each fob in these systems can be programmed to have a unique time delay. Some base stations, however, need to be capable of initiating actions in response to signals from hundreds, or even thousands, of fobs. Fleet vehicles may include such base stations. Assigning a unique time delay to each of these fobs is not practical due to increased system latency.